NASA's James Webb Space Telescope

PSF Simulation Tool: WebbPSF

Image of WebbPSF calculator


Simulated point spread functions for JWST can be produced using the WebbPSF package.  A library of precomputed PSFs is available if you would like to download one or two instances, but running the software yourself provides much more flexibility.

What does WebbPSF do?

PSFs are computed based on a supplied library of optical path difference (OPD) files consistent with the JWST optical error budget, including wavefront errors in the Optical Telescope Element (OTE) and in each instrument. 10 independent statistical realizations are provided for each. Using these, WebbPSF computes observed PSFs assuming Fraunhofer (far-field) propagation. WebbPSF provides:

  • Support for all of JWST's instruments.
  • PSF simulations for direct imaging and coronagraphic modes, and for non-redundant aperture masking mode on NIRISS.
  • Improved instrument properties such as normalized filter throughputs for NIRCam, NIRspec, and NIRISS, and detector pixel scales and orientations for all instruments.
  • Arbitrary oversampling of output PSFs
  • Quick calculations using optimized matrix Fourier transforms, the fast semi-analytic coronagraphy algorithm, and the FFTW3 library (optional).
  • Built-in functions for PSF evaluation such as producing radial profile plots, measuring encircled energy curves, FWHMs, etc.
  • A greatly improved graphical user interface.
  • An easy-to-use scripting interface for integration with other tools.

Limitations: The spectroscopy modes of NIRSpec and MIRI are not yet supported. Detector imperfections are likewise not included. The current OPD models do not support field-dependent wavefront error across the instrument FOVs. Future versions of WebbPSF and related software packages will address these issues.

Obtaining WebbPSF

WebbPSF is written in Python and should run on any platform that supports numpy/scipy/matplotlib. About 900 MB disk space is required, mostly for the simulated OPD map library.

Installation instructions and download links

Release notes

Software Documentation

WebbPSF documentation main page

Quick start

Scripting interface examples 

WebbPSF Feedback

WebbPSF was developed by Marshall Perrin, with contributions from other members of the Telescopes group at STScI. Please send any comments or suggestions to him at